Waveshines with falco took me forever to get down especialy because at first I would **** around with other characters so I became used to thier wavedash speed.
You could try only using falco for a while, practice pillars on level one foxes.
I used to play fox and falco and my timing was used fox's wavedash so my falco would just jump. Now that I only play falco whenever I do pick up fox for a min I do his wavedash a little to slow because I'm used to falco's so don't try to play both untill you have one 100% on lock.
Or my favorite way to practice shffl and wavehine is play a level 1 marth with 0.5 damage ratio. You can shuffle down air shine untill like 150% the jus waveshines him. He doesn't DI but he stay close so you just waveshines forward then back over and over.
Hope this helps and sorry if I'm confusing or make no sense. It's
Almost 3am and I'm very tired lol